<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    *{
          margin: 0;
          padding: 0;
    }
.page{
          height: 200px;
          display: flex;
          width: 400px;  
}
.left,.right{
            width: 200px;
            background-color: aqua;
            flex-shrink: 0;
            order: 1;
            flex: 1;
}
.content{
           background-color: brown;
           /* flex:1   */
           flex-shrink: 0;
           order: 2;
}
.left{
         order: 0;
}
.right{
          order: 2;
}
</style>
</head>
<body>
    <div class="page">
        <div class="content">主题内容</div>
        <div class="left">广告位</div>
        <div class="right">广告位</div>
    </div>
</body>
</html>